The invention relates generally to the field of inhalation drug therapy, and in particular to the inhalation of aerosolized chemical substances. In one aspect, the invention provides a portable inhaler having a cartridge for storing a chemical substance in a dry state and a liquid dispenser to introduce a liquid to the substance to form a solution. Immediately after formation of the solution, the inhaler aerosolizes the solution so that it may be administered to a patient.
The atomization of liquid medicaments is becoming a promising way to effectively deliver many medicaments to a patient. In particular there is a potential for pulmonary delivery of protein peptides and other biological entities. Many of these are easily degraded and become inactive if kept in a liquid form. Proteins and peptides often exhibit greater stability in the solid state. This results primarily from two factors. First, the concentration of water, a reactant in several protein degradation pathways, is reduced. See Stability of Protein Pharmaceuticals, M. C. Manning, K. Patel, and R. T. Borchardt, Phann. Res. 6, 903-918 (1989), the complete disclosure of which is herein incorporated by reference. Second, the proteins and other excipients are immobilized in the solid state. Water is a reactant in hydrolysis reactions, including peptide change and cleavage, and deamidation. Reducing the water concentration by freeze-drying or spray drying, reduces this reactant concentration and therefore the rates of these degradation pathways.
The mobility of the peptides or proteins, as well as other molecules in the formulation, are reduced in the solid or dry state. See Molecular Mobility of Amorphous Pharmaceutical Solids Below Their Glass Transition Temperatures, B. C. Hancock, S. L. Shamblin, and G. Zografi, Pharm. Res. 12, 799-806 (1995), the complete disclosure of which is herein incorporated by reference. For the peptides or proteins, this reduces the rate of intermolecular interactions as well as intramolecular conformational changes or fluctuations in conformation. Minimization of intermolecular interactions will reduce protein and peptide aggregation/precipitation, and will also reduce the rate of diffusion of chemical reactants to the protein or peptide which will slow the rate of chemical degradation pathways. Reduction in intramolecular conformational changes reduces the rate at which potentially reactive groups become available for chemical or intermolecular interaction. The rate of this reaction may decrease as the water concentration, and mobility of the protein, is reduced.
One way to produce protein in solid or dry state is to transform the liquid into a fine powder. When used for inhalation delivery, such powders should be composed of small particles with a mean mass diameter of 1 to 5 microns, with a tight particle size distribution. However, this requirement increases the processing and packaging cost of the dry powder. See also U.S. Pat. No. 5,654,007 entitled xe2x80x9cMethods and System for Processing Dispersible Fine Powdersxe2x80x9d and U.S. Pat. No. 5,458,135 entitled xe2x80x9cMethods and Devices for Delivering Aerosolized Medicamentsxe2x80x9d, the disclosures of which are incorporated herein by reference.
An easier way to transform a liquid solution to solid or dry form is to use a freeze drying process where a liquid solution is converted to a solid substance that can be readily reconstituted to a liquid solution by dissolving it with a liquid, such as water. Hence, one object of the present invention is to provide a way to store a solid substance and combine the solid substance the with a liquid to form a solution. Once the solution is formed, it is another object of the invention to rapidly transport the solution to an atomization device to allow the solution to be aerosolized for administration. In this way, the solution is aerosolized immediately after its reconstitution so that the degradation rate of the substance is reduced.
A variety of nebulization devices are available for atomizing liquid solutions. For example, one exemplary atomization apparatus is described in U.S. Pat. No. 5,164,740, issued to Ivri (xe2x80x9cthe ""740 patentxe2x80x9d), the complete disclosure of which is herein incorporated by reference. The ""740 patent describes an apparatus which comprises an ultrasonic transducer and an aperture plate attached to the transducer. The aperture plate includes tapered apertures which are employed to produce small liquid droplets. The transducer vibrates the plate at relatively high frequencies so that when the liquid is placed in contact with the rear surface of the aperture plate and the plate is vibrated, liquid droplets will be ejected through the apertures. The apparatus described in the ""740 patent has been instrumental in producing small liquid droplets without the need for placing a fluidic chamber in contact with the aperture plate, as in previously proposed designs. Instead, small volumes of liquid can be placed on the rear surface of the aperture plate and held to the rear surface by surface tension forces.
A modification of the ""740 apparatus is described in U.S. Pat. No. 5,586,550 (xe2x80x9cthe ""550 patentxe2x80x9d) and U.S. Pat. No. 5,758,637 (xe2x80x9cthe ""637 patentxe2x80x9d), the complete disclosures of which are herein incorporated by reference. These two references describe a liquid droplet generator which is particularly useful in producing a high flow of droplets in a narrow size distribution. As described in the ""550 patent, the use of a non-planar aperture plate is advantageous in allowing more of the apertures to eject liquid droplets. Furthermore, the liquid droplets may be formed within the range from about 1 xcexcm to about 5 xcexcm so that the apparatus will be useful for delivering drugs to the lungs.
Hence, it is a further objective of the invention to provide devices and methods to facilitate the transfer of liquid solutions (preferably those which have just been reconstituted) to such aerosolizing apparatus so that the solution may be atomized for inhalation. In so doing, one important consideration that should be addressed is the delivery of the proper dosage. Hence, it is still another object of the invention to ensure that the proper amount of liquid medicament is transferred to an aerosol generator so that a proper dosage may be delivered to the lungs.
The invention provides exemplary systems, apparatus and methods for reconstituting a solid phase substance, e.g., a substance that is in a dry state, with liquid to form a solution and for transporting the solution to an aerosol generator for subsequent atomization. In one exemplary embodiment, the system comprises a liquid dispenser, a cartridge containing a substance in a dry state, and an aerosol generator. In use, the cartridge is coupled to an outlet of the dispenser and the dispenser is operated to dispense liquid from the outlet and into the cartridge. The liquid then flows through the substance and exits the cartridge as a solution.
In an exemplary aspect, the cartridge is replaced and disposed after each use. After removal of the cartridge the user may optionally operate the liquid dispenser to deliver liquid to the aerosol generator for a subsequent cleaning cycle. In another exemplary aspect, a liquid outlet of the cartridge is positioned near the aerosol generator such that the solution is dispensed onto the aerosol generator and is readily available for atomization.
The Liquid Dispenser
In an exemplary embodiment, the liquid dispenser comprises a mechanical pump that is attached to a canister. The liquid dispenser is disposed within a housing of the inhaler and is configured to deliver a predetermined volume of liquid each time the mechanical pump is operated. The dispensed liquid then flows directly from the pump to the cartridge to form a solution which in turn is deposited on the aerosol generator.
In one particular aspect, the liquid is a saline solution or sterile water and may optionally contain an anti-microbial additive. As previously mentioned, the solid substance in the cartridge preferably comprises a chemical that is in the dry state which is reconstituted into a solution upon introduction of the liquid from the liquid dispenser.
In one particularly preferable aspect, the mechanical pump comprises a piston pump that is connected to the canister. The piston pump comprises a spring-loaded piston member that is slidable within a cylindrical member which defines a metering chamber. When the piston member is moved to a filling position, the metering chamber is filled with liquid from the canister. When released, the piston member moves to a dispensing position to dispense a known volume of liquid from the metering chamber. In this way, each time the pump is operated, a unit volume of liquid is dispensed from the piston pump.
In one particularly preferable aspect, movement of the piston member toward the filling position creates a vacuum inside the cylindrical member that gradually increases until the piston member reaches a point where a passage is provided between the piston member and the cylindrical member. At this point, the piston member has reached the filling position to allow liquid from the canister to be drawn by the vacuum into the metering chamber of the cylinder. At this point, the piston member is released and returns by the force of the spring back to the dispensing position. During the return travel of the piston member to the dispensing position, the liquid in the metering chamber is displaced through an outlet of the pump.
In another particular aspect, the piston pump is configured to deliver volumes of liquid in the range of about 10 xcexcL to about 50 xcexcL each time the pump is operated. In another aspect, the piston pump is configured such that it will dispense a full unit volume only if the user fully depresses the piston to the filling position. If the piston member is only partially depressed, no liquid will be dispensed. In this manner, partial dosing is prevented.
In still yet another aspect, the liquid dispenser further includes a valve which serves to eliminate the dead volume in the piston pump, thereby inhibiting microbial inflow into the liquid dispenser. The valve preferably comprises a tubular valve seat that is slidably disposed about a distal end of the piston member. In this way, the liquid within the metering chamber moves the tubular valve seat distally over the piston member to allow the liquid in the metering chamber to be dispensed by flowing between the piston member and the tubular valve seat when the piston member is moved toward the dispensing position. The tubular valve seat is also slidable within the cylindrical member, and the cylindrical member defines a stop to stop distal movement of the tubular valve seat relative to the piston member after the unit volume of liquid has been dispensed from the metering chamber. Further, when the spring forces the distal end of the piston member into a distal end of the tubular valve seat, a seal is provided between the piston member and the tubular valve seat to prevent microbial inflow into the piston pump. Hence, use of the tubular valve seat in combination with the piston member and the cylindrical member allows for a unit volume of the liquid within the piston pump to be dispensed and further provides a seal to prevent microbial inflow into the piston pump.
The Drug Cartridge
The cartridge of the invention allows for the storage of a chemical in a dry state. When a liquid is introduced into the cartridge, the chemical substance dissolves within the liquid to form a solution just prior to aerosolization of the solution.
In one exemplary embodiment, the cartridge comprises a housing having an inlet opening and an outlet opening. Disposed in the housing is a chemical substance which is in a dry state. As liquid flows through the housing, the substance dissolves and flows through the outlet opening as a solution. The chemical substance may be any one of a variety of chemical substances, such as proteins, peptides, small molecule chemical entities, genetic materials, and other macromolecules and small molecules used as pharmaceuticals. One particular substance is a lyophilized protein, such as interferon alpha or alpha 1 prolastin. The lyophilized substance is preferably held in a support structure to increase the surface area that is in contact with the liquid, thereby increasing the rate by which the substance is dissolved. The support structure is preferably configured to hold the lyophilized substance in a three-dimensional matrix so that the surface area of the substance that is contact with the liquid is increased. Exemplary types of support structures include open cell porous materials having many tortuous flow paths which enhance mixing so that the solution exiting from the outlet end is homogenized. Alternatively, the support structure may be constructed of a woven synthetic material, a metal screen, a stack of solid glass or plastic beads, and the like.
When used in connection with the aerosolizing apparatus of the invention, actuation of the liquid dispenser introduces liquid into the inlet opening, through the support structure to dissolve the substance, and out the outlet opening where it is disposed on the aerosol generator as a solution. The aerosol generator is then operated to aerosolize the solution. In this way, the substance is stored in a solid state until ready for use. As previously described, the flow of liquid from the liquid dispenser is produced during the return stroke of the piston member, i.e. as the piston member travels to the dispensing position. Since the return stroke is controlled by the spring, it is not dependent on the user. In this way, the flow rate is the same each time the liquid dispenser is operated, thereby providing a way to consistently and repeatedly reconstitute the solution.
In one particular aspect, the cartridge includes a coupling mechanism at the inlet opening to couple the cartridge to the liquid dispenser. In this way, the cartridge is configured to be removable from the liquid dispenser so that it may be removed following each use and discarded. In still another aspect, the cartridge is filled with the chemical substance while in a liquid state. The substance is then freeze dried and converted to a solid state while in the cartridge.
The Aerosol Generator
In an exemplary embodiment, the aerosol generator that is employed to aerosolize the solution from the cartridge is constructed in a manner similar to that described in U.S. Pat. Nos. 5,586,550 and 5,758,637, previously incorporated herein by reference. In brief, the aerosol generator comprises a vibratable member having a front surface, a rear surface, and a plurality of apertures which extend between the two surfaces. The apertures are preferably tapered as described in U.S. Pat. No. 5,164,740, previously incorporated herein by reference. In one particular aspect, the vibratable member is preferably hemispherical in shape, with the tapered apertures extending from the concave surface to the convex surface. In use, the solution from the cartridge is supplied to the rear surface of the vibratable member having the large opening. As the vibratable member is vibrated, the apertures emit the solution from the small openings on the front surface as an aerosolized spray. The user then simply inhales the aerosolized spray to supply the chemical to the patient""s lungs.
The invention further provides exemplary methods and apparatus for aerosolizing a solution. In one exemplary embodiment, an apparatus comprises a cartridge having a first chamber, a second chamber, and a moveable divider between the first and the second chambers. An exit opening is included in the cartridge and is in communication with the second chamber. A liquid is disposed in the first chamber, and a substance that is in a dry state is in the second chamber. The apparatus further includes a piston that is translatable within the cartridge to transfer the liquid from the first chamber and into the second chamber to form a solution. An aerosol generator is further provided and is disposed near the exit opening to receive the solution from the cartridge and produce an aerosolized solution. In this way, the substance may be maintained in a dry state as with other embodiments until ready for aerosolization. To form the solution, the piston is moved within the cartridge to force the liquid from the first chamber and into the second chamber. Further translation of the piston forces the recently formed solution from the second chamber and onto the aerosol generator where the solution is aerosolized.
In one particular aspect, the divider has a home position where a seal is formed between the divider and the cartridge. In this way, the liquid may be held in the first chamber until the piston is translated. Preferably, the cartridge includes at least one groove that is disposed at least part way between the first and second chambers. In this way, as the piston is moved within the first chamber, the liquid (which is generally incompressible) moves the divider toward the second chamber to allow the liquid to pass around the divider and into the second chamber. The groove preferably terminates at the second chamber so that when the piston moves the divider into the second chamber, a seal is formed between the cartridge and the divider to force the solution from the second chamber and out the exit opening.
In some cases, it may be desirable to draw the solution back into the first chamber to facilitate mixing. This can be accomplished by withdrawing the piston back through the first chamber to create a vacuum in the first chamber. To dispense the solution, the piston is translated back through the first and second chambers as previously described.
In one particular aspect, a filter is disposed across the exit opening to prevent larger particles from exiting the chamber and clogging the aerosol generator. In another aspect, the apparatus includes a motor to translate the piston. In this way, an aerosolized solution may be supplied to the patient simply by actuating the motor.